Magazine is the name for an item or place within which ammunition

Ammunition

Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...

 is stored. It is taken from the Arabic word "makahazin" meaning "warehouse".
Magazine is also a term used for a place where large quantities of ammunition are stored for later distribution, or an ammunition dump. This usage is less common.
In the early history of tube artillery

Artillery

Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 drawn by horses (and later by mechanized vehicles), ammunition was carried in separate unarmored wagons or vehicles.